1. Field of the Invention
The present invention relates to a cassette having a radiation image storage medium, and more specifically but not restricted to a cassette having a radiation image storage panel or plate for use in a radiation image recording and readout system, the storage panel including a sheet of stimulable phosphor, on which a latent image is recorded or stored that is formed by an imagewise radiation impinging thereon.
2. Description of the Prior Art
There have been known some kinds of phosphor which store, when exposed to a radiation, such as an X-ray, .alpha.-ray, .beta.-ray, .gamma.-ray or ultraviolet ray, to store a part of the energy of the radiation, and irradiate in association with the stored energy when stimulated afterwards with another radiation such as visible light. Such phosphors may often be referred to as stimulable phosphors.
The assignee of the patent application has proposed a radiation image recording and readout technique utilizing stimulable phosphors, in U.S. Pat. No. 4,258,264 and Japanese Patent Laid-Open Publication No. 11395/1981, for example. In accordance with the proposal, imagewise information carried by radiation transmitted through an object, such as a living body, is first recorded on a sheet of stimulable phosphor, which is then scanned with a stimulative ray generated by a laser, for example, to irradiate rays associated with the recorded information. The emitted rays are sensed by a photoelectric conversion device, that produces a time-serial video signal carrying the imagewise information. The video signal is used to produce a visual image associated with the image information carried therein on a recording medium, such as a sheet of photosensitive material, and/or a cathode-ray tube (CRT) display, for example.
In an application of the above-mentioned technique to medical diagnosis, for example, radiation image storage panels or plates should in practice be maintained in the dark throughout, before and after shooting a radiation image until an image stored therein has been produced as a visual picture, so as not to damage the image stored in the sheet. The stored image would otherwise be damaged by components of natural radiation which have a wavelength ranging from 450 to 1,100 nanometers stimulable to the phosphor as well as ultraviolet rays which may cause radiation energy to be stored as noise in the stimulable phosphor sheet, since such components and rays allow a portion of the stored energy to be dissipated and are stored as noise in the phosphor material. Care should therefore be taken to deal with stimulable phosphor sheets in the dark, and those sheets are in practice enclosed in enclosures or containers, such as a cassette, which contains a single sheet of stimulable phosphor, or a magazine, which contains a plurality of stimulable phosphor sheets.
In hospitals, it is often required to handle a large amount of stimulable phosphor sheets for image processing in a relatively short period of time. Such enclosures having a stimulable phosphor sheet or sheets are transferred from radiation exposure rooms or sites to a radiation image processing center or station. The significant amount of phosphor sheets collected at the center may raise a serious problem of how to identify the respective sheets thus collected.
One of the solutions to the problem is to provide respective stimulable phosphor sheets with specific identifications, such as identification codes or serial numbers, associated with data or particulars related to objects whose images are stored in the phosphor sheets, and enter such information into a computer system in the radiation image processing center. Such data may contain object data specifying an object or patient under radiation exposure, such as name, sex, date of birth and the like, as well as exposure data associated with a radiation exposure, such as data and time of exposure, amount of a radiation irradiated, imaged portion of a body, and the like. When images stored in stimulable phosphor sheets are afterwards read out and produced as visual images, data associated with the sheets are searched for by indexing identifications alotted thereto in the central computer system.
In the case of a cassette, including a single plate of stimulable phosphor, the cassette may be provided with an indication representative of an identification for the phosphor plate contained therein. However, this does not assure a phosphor sheet enclosed in a cassette being associated with the indication provided on the cassette, and it is difficult to know from the outside whether or not a cassette contains a stimulable phosphor sheet.
In the case of a magazine, containing a plurality of stimulable phosphor sheets therein, it is also difficult to determine which sheets are associated with respective indications provided on a magazine and representative of identifications for the respective sheets. If one takes a phospher sheet or sheets out of a cassette or magazine, she will identify the sheet or sheets by means of an identification code indicated thereon, but this is inefficient and increases the possibility of exposing the phosphor sheets to undesired visible, infrared and ultraviolet rays or other radiations, thereby causing noise in an image recorded thereon.